NEUTRINOS
The history and the present
Presentation by Janna de Wit and Tommaso Isolabella
Colorless, electrically neutral
3 families
Left-handed
Oscillate
Small non-zero mass
• HISTORY
OUTLINE
• THEORY
• EXPERIMENTS
• SUMMARY
1930
1933
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1967
1968
1985
1989
1998
2000
• Observation of 𝜈 and 𝜈
• Left-handedness of 𝜈
HISTORY
• Discovery of different species
• ‘Solar neutrino problem’
• ‘Atmospheric neutrino deficit’
• Oscillations
2001
1930
1933
1956
1957
1959
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1967
1968
1985
1989
1998
2000
First concept of ν
Chadwick showed that electrons were emitted in a continuous spectrum.
Early understanding of beta decay:
6
𝐻𝑒 → 6𝐿𝑖 + 𝑒 −
𝑛 → 𝑝 + 𝑒−
1. Energy of 𝑒 − in continuous spectrum, energy not conserved
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
First concept of ν
Chadwick showed that electrons were emitted in a continuous spectrum.
Early understanding of beta decay:
6
𝐻𝑒 → 6𝐿𝑖 + 𝑒 −
𝑛 → 𝑝 + 𝑒−
Spin:
1
2
1
1
→2+2
1. Energy of 𝑒 − in continuous spectrum, energy not conserved
2. Angular momentum not conserved
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
First concept of ν
1
Pauli’s understanding of beta decay:
6
𝐻𝑒 → 6𝐿𝑖 + 𝑒 − + 𝜈
𝑛 → 𝑝 + 𝑒− + 𝜈
He called it the neutron
1
Zero charge, spin 2
1989
1998
2000
2001
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1998
Fermi incorporates neutrino into theory
1932 Chadwick discovers the neutron.
1933 Fermi writes down the correct theory for beta decay.
Neutrino
2000
2001
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1985
1989
1998
Reines and Cowan observe (anti) neutrino
Beta decay:
𝑛 → 𝑝 + 𝑒− + 𝜈
Predicted inverse beta-decay:
𝜈 + 𝑝 → 𝑛 + 𝑒+
2000
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
Reines and Cowan observe (anti) neutrino
Beta decay:
𝑛 → 𝑝 + 𝑒− + 𝜈
Predicted inverse beta-decay:
𝜈 + 𝑝 → 𝑛 + 𝑒+
• 𝜈 source: reactor
• Target: tank of water, with Cadmium
• Cadmium absorbs neutron, γ-ray
• 𝑒 + 𝑒 − annihilate, γ-ray
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
Reines and Cowan observe (anti) neutrino
Beta decay:
𝑛 → 𝑝 + 𝑒− + 𝜈
Predicted inverse beta-decay:
𝜈 + 𝑝 → 𝑛 + 𝑒+
• 3 𝝂 per hour
• Disappeared when reactor was shut off
2001
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1998
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Goldhaber finds 𝜈 to be left-handed
One year before: Wu finds parity is not conserved in the weak interactions.
If mass is 0, chirality = helicity
Helicity:
𝑆 ↑↓ 𝑝 LH
𝑆 ↑↑ 𝑝 RH
2001
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Goldhaber finds 𝜈 to be left-handed
Look at electron capture of Europium:
Eu
𝑝
←
+
𝑒−
𝑆
0
→
→
ν
←
+
←←
←←
Sm*
Sm* →
→
→
←←
Sm
0
+
γ
→
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
Goldhaber finds 𝜈 to be left-handed
Look at electron capture of Europium:
𝑝
←
𝐸𝑢𝑒
𝑆
0
→
→
ν
←
+
←←
←←
Sm*
Sm* →
→
→
←←
Sm
0
+
γ
→
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
Goldhaber finds 𝜈 to be left-handed
Look at electron capture of Europium:
𝑝
←
𝐸𝑢𝑒
𝑝
0
→
→
ν
←
+
←←
←←
Sm*
Sm* →
→
→
←←
Sm
0
+
γ
→
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
Goldhaber finds 𝜈 to be left-handed
Look at electron capture of Europium:
𝑆
←
𝐸𝑢𝑒
𝑝
0
→
→
ν
←
+
←←
←←
Sm*
Sm* →
→
→
←←
Sm
0
+
γ
→
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
Goldhaber finds 𝜈 to be left-handed
Look at electron capture of Europium:
LH
𝑆
←
𝐸𝑢𝑒
𝑝
0
LH
→
→
ν
←
+
←←
←←
Sm*
Sm* →
→
→
←←
Sm
0
+
γ
→
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
Goldhaber finds 𝜈 to be left-handed
Look at electron capture of Europium:
𝑆
→
𝐸𝑢𝑒
𝑝
0
←
→
ν
←
+
→→
→→
Sm*
Sm* →
→
→
→→
Sm
0
+
γ
→
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
2000
Goldhaber finds 𝜈 to be left-handed
Look at electron capture of Europium:
RH
𝑆
→
𝐸𝑢𝑒
𝑝
0
RH
←
→
ν
←
+
→→
→→
Sm*
Sm* →
→
→
→→
Sm
0
+
γ
→
2001
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1933
1956
1957
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1967
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1985
1989
1998
Goldhaber finds 𝜈 to be left-handed
Helicity (𝜈) = Helicity (γ)
2000
2001
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Goldhaber finds 𝜈 to be left-handed
Helicity (𝜈) = Helicity (γ)
𝑩 ↑ electron magnet has 𝑆 ↓
• Photon with 𝑆 ↑ : able to flip spin electron
It loses energy
Not able to excite target
• Photon with 𝑆 ↓ : likely to pass
Able to excite target
• Test for RH
2001
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2001
Goldhaber finds 𝜈 to be left-handed
Helicity (𝜈) = Helicity (γ)
𝑩 ↑ electron magnet has 𝑆 ↓
• Count events for two different polarizations
• Turned out to be left-handed!
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Davis and Harmer suggest difference 𝜈 and 𝜈
Is 𝜈 its own antiparticle?
2000
2001
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1998
Davis and Harmer suggest difference 𝜈 and 𝜈
Is 𝜈 its own antiparticle?
Beta decay:
𝑛 → 𝑝 + 𝑒− + 𝜈
Neutrino capture:
𝜈 + 37𝐶𝑙 →
37
𝐴𝑟 + 𝑒 −
2000
2001
1930
1933
1956
1957
1959
1962
1967
1968
1985
1989
1998
Davis and Harmer suggest difference 𝜈 and 𝜈
Is 𝜈 its own antiparticle?
Beta decay:
𝑛 → 𝑝 + 𝑒− + 𝜈
Neutrino capture:
𝜈 + 37𝐶𝑙 →
37
𝐴𝑟 + 𝑒 −
According to ‘law of lepton number conservation’:
𝑁𝑙 + 𝑁𝑙 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
2000
2001
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Davis and Harmer suggest difference 𝜈 and 𝜈
Is 𝜈 its own antiparticle?
• They put a detector containing Chlorine near a reactor
(source of 𝜈)
𝜈 + 37𝐶𝑙 →
37
𝐴𝑟 + 𝑒 −
• No extra Argon when reactors were operating
• 𝝂≠𝝂
2000
2001
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𝜈𝜇 is discovered
Lederman, Schwartz and Steinberger
Pion decay:
𝜋 →𝜇+𝜈
• Hit target with protons → pions
• Get rid of background → pure neutrino beam
• Look for reaction:
𝜈𝜇 + 𝑛 → 𝑝 + 𝜇−
𝜈𝑒 + 𝑛 → 𝑝 + 𝑒 −
• Tracks they observed suggested that 𝝂𝝁 ≠ 𝝂𝒆
2000
2001
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2001
Pontecorvo suggests neutrino oscillations
Standard Model:
Masses of the neutrinos are zero.
Pontecorvo:
If masses of neutrinos are nonzero:
Already observed:
𝜈𝑒 ⇆ 𝜈𝜇
𝐾0 ⇆ 𝐾0
Solar model:
𝜈𝑒 should be coming from the sun
Neutrino flux must be two times smaller
1930
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2001
Pontecorvo suggests neutrino oscillations
Standard Model:
Masses of the neutrinos are zero.
Pontecorvo:
If masses of neutrinos are nonzero:
Already observed:
𝜈𝑒 ⇆ 𝜈𝜇
𝐾0 ⇆ 𝐾0
Solar model:
𝑝 + 𝑝 → 𝑑 + 𝑒 + + 𝜈𝑒
Neutrino flux must be two times smaller.
He anticipated the ‘solar neutrino problem’ before it was observed!
1930
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2000
2001
Pontecorvo suggests neutrino oscillations
Standard Model:
Masses of the neutrinos are zero.
Pontecorvo:
If masses of neutrinos are nonzero:
Already observed:
𝜈𝑒 ⇆ 𝜈𝜇
𝐾0 ⇆ 𝐾0
Solar model:
𝑝 + 𝑝 → 𝑑 + 𝑒 + + 𝜈𝑒
Neutrino flux must be two times smaller.
He anticipated the ‘solar neutrino problem’ before it was observed!
1930
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1967
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1985
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1998
Davis observes ‘solar neutrino problem’
• Tank with dry-cleaning fluid
• Rich in Chlorine
𝜈𝑒 + 37𝐶𝑙 →
37
𝐴𝑟 + 𝑒 −
1
• Davis results ≈ 3 of theoretical values
→ Either solar model is wrong, or neutrinos oscillate.
2000
2001
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‘Atmospheric neutrino deficit’ is observed
•
IMB and Kamiokande
•
Looked at atmospheric neutrinos:
•
•
Cosmic ray collide with atmosphere
Shower of mostly pions:
𝜋 − → 𝜇− + 𝜈𝜇
𝜇 − → 𝑒 − + 𝜈𝜇 + 𝜈𝑒
•
Prediction flux ratio:
𝑁(𝜈𝜇 +𝜈𝜇 )
𝑁(𝜈𝑒 +𝜈𝑒 )
2
=1
2000
2001
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1998
‘Atmospheric neutrino deficit’ is observed
• Measure upward and downward going 𝜈
• 𝜈 is expected to be uniform
• Deficit in upward 𝜈𝜇
→ ‘Atmospheric neutrino deficit’
• Could indicate neutrino oscillation
• However, larger detectors were needed
2000
2001
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Only 3 families
LEP: accelerated 𝑒 + and 𝑒 −
When 𝑍 0 would ‘disappear’ → 𝜈 𝜈 are created
1998
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Only 3 families
[Source: The ALEPH Collaboration et al., Precision Electroweak Measurements on the Z Resonance, Physics Reports 427 (2006) 257]
2001
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Official confirmation ‘atmospheric neutrino deficit’
• Super-Kamiokande (Kajita and team)
• Already confirmed ‘solar neutrino problem’
• Now also confirmed ‘atmospheric neutrino deficit’
2001
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1989
1998
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Official confirmation ‘atmospheric neutrino deficit’
• Super-Kamiokande (Kajita and team)
• Already confirmed ‘solar neutrino problem’
• Now also confirmed ‘atmospheric neutrino deficit’
2001
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1989
DONUT collaboration observes 𝜈𝜏
• Once τ was discovered, physicist started looking for the 𝜈𝜏
• Took more than two decades!
• Similar as 𝜈𝜇 :
•
•
•
•
protons hit target
charmed mesons → decay into 𝜈𝜏
Lose background → neutrino beam
Look for τ tracks
𝜈𝜏 + 𝑛 → 𝑝 + 𝜏 −
1998
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1998
Solution of ‘solar neutrino problem’
• SNO (McDonald and team)
• Underground detector using heavy water
(D2 O)
• Makes it sensitive for 2 reactions
(one through which all 𝜈 interact and
one through which only the 𝜈𝑒 interacts)
• Measure oscillations directly
2000
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Solution of ‘solar neutrino problem’
• Charged current:
•
•
𝜈𝑒 converts n into p
𝑒 is emitted, Cherenkov radiation
• Neutral current:
•
•
•
𝜈 dissociates deuteron
n is captured again
γ ray is emitted
• Elastic scattering:
•
•
•
𝜈 collides with atomic 𝑒, Cherenkov radiation
𝜈𝜏 and 𝜈𝜇 only interact via 𝑍 0
𝜈𝑒 also via 𝑊 ±
• Results agreed with neutrino oscillations!
2000
2001
THEORY
• Neutrino oscillations
• CP violation
Neutrino oscillations
Mass eigenstates and flavor eigenstates related by the PMNS
matrix:
𝑈1𝑒
𝜈1
𝜈2 = 𝑈2𝑒
𝜈3
𝑈3𝑒
𝑈1𝜇
𝑈2𝜇
𝑈3𝜇
𝑈1𝜏
𝑈2𝜏
𝑈3𝜏
𝜈𝑒
𝜈𝜇
𝜈𝜏
• PMNS matrix not identity
• Mass eigenstates differ from flavor eigenstates
Neutrino oscillations
In a 2 neutrino framework one finds:
𝜈1
𝑐𝑜𝑠𝜃
=
𝜈2
−𝑠𝑖𝑛𝜃
𝑃 𝜈𝑒 → 𝜈𝜇 =
𝑠𝑖𝑛2
2𝜃
𝑠𝑖𝑛𝜃
𝑐𝑜𝑠𝜃
𝜈𝑒
𝜈𝜇
𝑚1 2 − 𝑚2 2 𝐿
4𝐸𝜈
𝑠𝑖𝑛2
1
Therefore 𝜆𝑜𝑠𝑐 ∝ Δ𝑚2
Neutrino oscillations
• Neutrinos are required to have mass in order to give rise to oscillations
• Cosmological measurements show that:
𝜈 𝑚𝜈
•
< 1 𝑒𝑉
Experiments so far have only measured Δ𝑚2 and not the actual masses
Neutrino oscillations
Mass hierarchy
Δ𝑚21 2 ≈ 8,5 × 10−5 𝑒𝑉 2
|Δ𝑚32 2 | ≈ 2 × 10−3 𝑒𝑉 2
CP violation
Operating in a 3-neutrino framework
𝑃 𝜈𝑒 → 𝜈𝜇 = 𝑃(𝜈𝑒 → 𝜈𝜇 )
∗
Therefore, unless the PMNS matrix elements are real,
𝑃(𝜈𝑒 → 𝜈𝜇 ) ≠ 𝑃 𝜈𝑒 → 𝜈𝜇
CP violation
How can we take this into account?
• Express PMNS matrix in terms of a phase 𝑒 𝑖𝛿𝐶𝑃
• If 𝛿𝐶𝑃 = 0 or 𝛿𝐶𝑃 = 𝜋, matrix elements are real
• Ongoing experimental efforts to measure this phase
• Super Kamiokande
• Borexino
EXPERIMENTS
• ANTARES
• COBRA
• IceCube
Experiments
Super Kamiokande
• Huge water tank filled with 50000 tons of pure water, surrounded by PMTs
• Neutrinos interact with neutrons or protons and produce Cherenkov radiation
• Mainly detects 𝜈𝑒 and 𝜈𝜇
Main events in SK:
𝜈𝑒,𝜇 + 𝑛 → 𝑝 + 𝑒 − /𝜇−
𝜈𝑒,𝜇 + 𝑛 → 𝑝 + 𝑒 + /𝜇+
Experiments
Super Kamiokande
What are they looking for?
•
•
•
•
Solar neutrinos
Atmospheric neutrinos
Supernovae neutrinos
Long-baseline neutrinos (long-baseline experiments)
Experiments
Super Kamiokande
Supernovae neutrinos
•
•
•
•
Neutrinos from supernovae reach Earth before EM radiation
Real-time supernova neutrino boost monitor
Possibility to measure direction of incoming neutrinos
Prediction of SN location
Experiments
Super Kamiokande
Long-baseline neutrinos
• T2K (Tokai to Kamioka) is an experiment aimed at studying muon neutrinos
produced in Tokai and travelling all the way to Super Kamiokande
• Tokai and Kamioka are separated by 295 km
• Neutrinos coming from Tokai are useful for studying the phenomenon of
oscillations
Experiments
Borexino
• Tank filled with scintillator liquid and
surrounded by PMT
• Studies low energy neutrinos (sub-MeV)
• Detects neutrinos through their elastic
scattering with electrons
Experiments
Borexino
What are they looking for?
• Low-energy solar neutrinos coming from
7
𝐵𝑒, monocromatic at 863 keV
• Geoneutrinos
Experiments
T2K and CP violation
Experiments
Super Kamiokande
Long-baseline neutrinos
• T2K (Tokai to Kamioka) is an experiment aimed at studying muon neutrinos
produced in Tokai and travelling all the way to Super Kamiokande
• Tokai and Kamioka are separated by 295 km
• Neutrinos coming from Tokai are useful for studying the phenomenon of
oscillations
Experiments
T2K and CP violation
• Long history of discoveries
• Weakly interacting, makes it difficult
SUMMARY
• Oscillations require neutrinos to have
mass
• Neutrinos can be an efficient probe into
CP violation
• Experiments are being done to
investigate further
References
The ALEPH Collaboration et al., Precision Electroweak Measurements on the Z Resonance, Physics Reports 427 (2006) 257
Maurice Goldhaber, Lee Grodzins und Andrew W. Sunyar, Helicity of Neutrinos, Physical Review. 109, Nr. 3, 1958, S. 1015-1017
Fourth Quantum Universe Symposium, conference talk Alain Blondel, Neutrino physics, now and in the future, April 17, 2014
C.L. Cowan Jr., F. Reines, F.B. Harrison, H.W. Kruse, A.D. McGuire (20 juli 1956), Detection of the Free Neutrino: a Confirmation, Science 124: 103-104
R. Davis, Jr., and D.S. Harmer, Attempt to Observe the Cl-73 Ar-37 reaction induced by reactor antineutrinos, Bulletin of the American Physical Society, 4, 217 (1959)
G. Danby; J.-M. Gaillard; K. Goulianos; L. M. Lederman; N. B. Mistry; M. Schwartz; J. Steinberger (1962). "Observation of high-energy neutrino reactions and the existence of
two kinds of neutrinos". Physical Review Letters. 9: 36
B. Pontecorvo, “Neutrino experiments and the question of leptonic-charge conservation,” Zhurnal Eksperimental'noi i Teoreticheskoi Fiziki, vol. 53, pp. 1717–1725, 1967,
Soviet Physics—JETP, vol. 26, p. 984, 1968
B. T. Cleveland, T. Daily, R. Davis Jr. et al., “Measurement of the solar electron neutrino flux with the homestake chlorine detector,” The Astrophysical Journal, vol. 496, no. 1,
article 505, 1998
Edward Kearns, Takaaki Kajita, and Yoji Totsuka: "Detecting Massive Neutrinos". Scientific American, August 1999
K. Kodama et al. (DONUT Collaboration) (2001). "Observation of tau neutrino interactions". Physics Letters B. 504 (3): 218
Ahmad, QR; et al. (2001). "Measurement of the Rate of νe + d → p + p + e− Interactions Produced by 8B Solar Neutrinos at the Sudbury Neutrino Observatory". Physical
Review Letters. 87 (7): 071301
References
M. Tegmark et al., Cosmological Constraints from the SDSS Luminous Red Galaxies
K. Abe et al., Real-Time Supernova Neutrino Burst Monitor at Super-Kamiokande
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Solution of ‘solar neutrino problem’
2000
2001
Experiments
•
𝜈𝑒 produced in Earth’s crust and mantle in decays of radioactive
Th, U and K
• Detectable through the inverse beta decay 𝜈 + 𝑝 → 𝑛 + 𝑒 +
• Recently observed by Borexino at 4σ
• Information about the distribution of radioactive elements